A 3G network architecture defined by the 3rd Generation Partnership Project (3GPP) in the Wideband Code Division Multiple Access (WCDMA) R4 standard mainly includes a radio access network (RAN), a core network and a bearer network (Backbone). A generalized RAN includes an air interface, that is, a Uu interface, between a terminal and a base station, and an Iub interface between the base station and a base station controller. From the perspective of transmission and bearing, an RAN generally refers to an aggregation network between a base station and a base station controller.
With the development of mobile networks from 2G technologies to 3G technologies and then to Long Term Evolution (LTE) technologies, mobile communications networks evolve towards the direction of broadband, packetization, and flattening, and mobile all Internet Protocol (IP) (ALL IP) networks have become an irreversible trend. RANs are also faced with the trend of transforming from conventional time division multiplexing (TDM)/asynchronous transfer mode (ATM) RANs to IP RANs. IP RANs based on an IP/multiprotocol label switching (MPLS) packet data technology have a higher bandwidth, support statistical multiplexing of a data service, can better support a future broadband mobile service, use a same technology as an IP backbone, and have better consistency and integration with the backbone; therefore, the IP RANs are widely applied. An IP RAN based on the IP/MPLS technology mainly includes an access ring formed on a base station side by ATNs or devices of other types, and an aggregation ring formed by CXs or devices of other types. Generally, each device on an aggregation ring may access to 10 to 20 access rings. Each access ring is formed by about 10 ATNs and the like. Generally, two high-end CXs or devices of other types are placed on the aggregation ring to serve as gateways, and are connected to a core network. An ATN or another device on the access ring is referred to as a cell site gateway (Cell Site Gateway, abbreviated as CSG) or a multi-service transport gateway (Multi-Service Transport Gateway, abbreviated as MSTG). A CX or a device of another type on the aggregation ring is referred to as a radio network controller site gateway (RNC Site Gateway, abbreviated as RSG) or a multi-service aggregation gateway (Multi-Service Aggregation Gateway, abbreviated as MSAG). A device located both on the access ring and on the aggregation ring is a core router (Provider Router), that is, a P device, in an MPLS virtual private network (Virtual Private Network, abbreviated as VPN); and another device located on the access ring or the aggregation ring is a provider edge (Provider Edge, abbreviated as PE) in the MPLS VPN.
In an IP RAN network, in order to enable the MPLS technology to better meet requirements of an access network, the International Telecommunication Union-Telecommunication Standardization Sector (ITU Telecommunication Standardization Sector, abbreviated as ITU-T) and the Internet Engineering Task Force (Internet Engineering Task Force, abbreviated as IETF) jointly developed a MPLS Transport Profile (Transport Profile for MPLS, abbreviated as MPLS-TP) technology by extending a conventional MPLS technology, which mainly excludes some features in the conventional MPLS technology that are not applicable to an access network scenario and adds some new features to adapt to the requirements of the access network. For example, in the MPLS-TP technology, a complex control protocol suite defined in conventional MPLS is discarded, so that the degree of coupling between the MPLS and the IP is reduced; and the data plane is simplified, penultimate hop popping (Penultimate Hop Popping, abbreviated as PHP), equal-cost multipath (Equal Cost Multi Path, abbreviated as ECMP), label merging, refined packet discard processing, and the like are removed, technologies, such as a pseudo wire (Pseudo Wire, abbreviated as PW) multi-service bearing technology, and a time division multiplexing (Time-Division Multiplexing, abbreviated as TDM) service emulation technology are added, and operation, administration and maintenance (Operation Administration and Maintenance, abbreviated as OAM) and protection restoration functions are added.
According to the design of the MPLS-TP, OAM and protection technologies of the MPLS-TP are used for a Layer 2 service implemented by using an MPLS TE tunnel and a pseudo wire emulation edge-to-edge (Pseudo Wire Emulation Edge-toEdge, abbreviated as PWE3) service. Because both the Layer 2 service implemented by using the MPLS TE tunnel and the PWE3 service are point-to-point, the MPLS TE tunnel or a PW can be directly identified by using a VPN private network label, so as to perform explicit fault location or performance statistics; while a Layer 3 VPN (Layer 3 VPN, abbreviated as L3VPN) service is a multipoint to point service, a tail end cannot effectively identify a source end of the service.